Wireless transmitters used in cellular, trunked, point-to-point and other wireless communication applications often utilize automatic output controllers to control and stabilize transmitter output during transmission and to improve radio link performance. In mobile cellular communication terminals, for example, variations in output power may result in inadequate signal power at the base station receiver. Output variations also cause variations in current drain, resulting in unnecessary heat dissipation and in reduced talk-time performance in battery-powered mobile communication devices.
In most communications applications, the automatic output controller (AOC) system provides a variable output. In cellular communications systems, for example, the output of the cellular handset is controlled to a variable power level requested by the base station. In time division multiple access systems, the transmitter operates in a burst mode. In burst mode transmitters, it is important that the power level be controlled smoothly and accurately during ramp-up and ramp-down of the transmission burst in order produce the required output, while avoiding out of band spectral emissions. In amplitude modulation communications systems, the transmitter output level varies according to the transmission data. A precise output level is needed to accurately demodulate the signal and to avoid out of band spectral emissions.
In most communications equipment, the output power is factory calibrated for some particular load impedance, typically 50Ω. In many wireless applications, it is important that the transmitter output level and current drain be controlled accurately while the load impedance varies. In wireless communication devices, load impedance variation is caused largely by variable antenna impedance. In mobile telephone handsets, for instance, the antenna input impedance varies with changes in the proximity of the handset to the user.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below.